Use sizeof(buffer) instead of duplicating the constants to ensure they won't be wrong.
Use sizeof(buffer) instead of duplicating the constants to ensure they won't
be wrong.

The real change is to pass (bufsz - 1) to PyOS_ascii_formatd and 1
to strncat.  strncat copies n+1 bytes from src (not dest).

Reported by Klocwork #58.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator